The present invention relates generally to optical disk reproduction apparatus such as DVD (Digital Versatile Disk) players, and more particularly to an improved optical disk reproduction apparatus which is capable of high-quality reproduction of recorded information at each individual radial position of an optical disk with minimized errors without undesirably suspending the reproduction.
On DVDs and some other types of optical disks, information is recorded using the so-called xe2x80x9cmark length recording schemexe2x80x9d. In a reproduced RF signal waveform output from an optical pickup reading out the information recorded with such a mark length recording scheme, higher-frequency components (i.e., signals of smaller pulse widths) would present lower signal levels. Thus, if each reproduced RF signal from the optical pickup is input into a slicer and binarized thereby, as it is, using a predetermined slice level, great jitter tend to occur, thus resulting in many errors. For this reason, it has been conventional to first input the reproduced RF signal into a waveform equalization circuit so that the reproduced RF signal is binarized by the slicer with the levels of the higher-frequency components raised to a predetermined degree, to thereby reduce the undesired jitter. Further, some of the conventional DVD players contain a jitter detection circuit, and performs test reproduction of the optical disk with respect to an innermost location of the optical disk prior to actual or non-test reproduction of the disk. Through the test reproduction, waveform equalization characteristics of the waveform equalization circuit are adjusted to optimize (e.g., minimize) the jitter level by the jitter detection circuit. During the subsequent actual reproduction, the recorded information on the entire optical disk is reproduced with the waveform equalization characteristics fixed at the adjusted values or settings.
Among various schemes for reproducing a DVD or other type of optical disk with information recorded at a constant linear velocity is one which can reproduce the recorded information at high speed by rotating the optical disk at a constant angular velocity and eliminate a need for variably controlling the rotating speed in accordance with a radial position or address, on the optical disk, of each location to be reproduced via the optical pickup (i.e., a radial position traversed by the optical pickup). In such constant-angular-velocity reproduction of the optical disk with information recorded at a constant linear velocity (i.e., CLV optical disk), the data transfer rate differs between the inner and outer regions of the optical diskxe2x80x94the difference in the data transfer rate is normally compensated for by a buffer memoryxe2x80x94, so that there would occur great variations in the amplitudes of the high-frequency components of the reproduced RF signal waveform (particularly, the amplitude of 3T-pit signals in the DVD case). Thus, with the conventionally-known technique of adjusting the waveform equalization characteristics of the waveform equalization circuit through the test reproduction performed with respect to innermost location of the optical disk and then fixedly using the thus-adjusted waveform equalization characteristics, there would be countered the problem that the jitter increase as the reproduction proceeds toward the outer circumferential region of the disk.
Further, if the optical disk has a warp, the reproducing laser light would get out of focus, which would also lead to an increased jitter level. To reduce the jitter caused by the disk warp, it is generally effective to perform focus adjustment, such as focus balance adjustment or focus error adjustment, and also adjust the waveform equalization characteristics of the waveform equalization circuit. However, because the disk warp, if any, generally becomes greater in the inner-to-outer direction of the optical disk, the conventionally-known technique of adjusting the waveform equalization characteristics of the waveform equalization circuit through the test reproduction with respect to innermost location and then fixedly using the adjusted waveform equalization characteristics would present the problem the jitter level increases as the reproduction proceeds toward the outer circumferential region of the disk.
One possible solution to the above-mentioned jitter problem in the case where the CLV optical disk is reproduced at a constant angular velocity or where a warped disk is reproduced may be to perform the focus adjustment and waveform equalization characteristic adjustment, on a real-time basis, by detecting the jitter while the optical disk is being read via the optical pickup. However, because the focus adjustment and waveform equalization characteristic adjustment is each one form of control for finding optimum values or settings capable of providing an optimal (e.g., minimal) jitter level while variously changing the settings, it unavoidably passes, during the course of the adjustment, some locations where the jitter level is unsatisfactory, with the result that the real-time adjustment can not be performed appropriately while allowing the optical disk to be read via the optical pickup without suspension.
In view of the foregoing, it is an object of the present invention to provide an improved optical disk reproduction apparatus which, even where a constant-liner-velocity (CLV) disk is to be reproduced at a constant angular velocity or a warped disk is to be reproduced, is capable of high-quality reproduction of recorded information from the optical disk by modifying focus adjustment or waveform equalization characteristic adjustment to optimal settings, without suspending the reproduction, so as to achieve an optimum jitter level at each individual radial position of the disk.
To accomplish the above-mentioned object, the present invention provides an optical disk reproduction apparatus which comprises: an optical pickup arranged to read out recorded information from an optical disk; a waveform equalization section arranged to perform a waveform equalization process on a reproduced RF signal that is generated on the basis of the recorded information read out by the optical pickup; a jitter detection section arranged to detect jitter of the reproduced RF signal having been subjected to the waveform equalization process; and a control section. The control section is arranged to perform test reproduction of the optical disk with respect to a plurality of testing radial locations of the optical disk prior to actual reproduction of the optical disk, adjust a waveform equalization characteristic of the waveform equalization section to an optimal setting so as to optimize the jitter of the reproduced RF signal detected by the jitter detection section at each of the testing radial locations of the optical disk, and during the actual reproduction of the optical disk, adjust the waveform equalization characteristic of the waveform equalization section to an optimal setting that is predicted, from the optimal setting determined by the test reproduction, in accordance with a changing radial position of the optical disk to be reproduced via the optical pickup. In the present invention, an optimal setting of the waveform equalization characteristic is predicted and set, for each radial position of the optical disk, on the basis of the optimal setting determined by the test reproduction, and thus there can always be provided an optimal waveform equalization characteristic, for each radial position of the optical disk, capable of optimizing (e.g., minimizing) the jitter, without suspending the reproduction.
The optical disk reproduction apparatus of the present invention further comprises a focus adjustment section arranged to perform a focus adjustment process for adjusting either one or both of a focus balance and focus offset by use of two focus-error-detecting signals generated on the basis of the recorded information read out by the optical pickup. In this case, the control section, during the test reproduction, adjusts the focus adjustment section to an optimal setting at each of the testing radial locations, prior to adjustment of the waveform equalization characteristic, so as to optimize the jitter of the reproduced RF signal detected by the jitter detection section. During the actual reproduction, the control section performs further control to adjust the focus adjustment section to an optimal setting that is predicted, from the optimal setting determined by the test reproduction, in accordance with a radial position or address, on the optical disk, of each location to be reproduced via the optical pickup. Thus, if the optical disk has a radial warp, it can be reproduced appropriately with optimized (e.g., minimized) jitter at each radial location thereof. In this case, the control section may store, into a memory, the optimal setting of the focus adjustment section determined by the test reproduction, and during the actual reproduction, the control section may arithmetically predict an optimal setting of the focus adjustment section, on the basis of the optimal setting of the focus adjustment section stored in the memory, in accordance with the radial position, on the optical disk, of each reproduced location.
Whereas the above-mentioned inventive optical disk reproduction apparatus can be advantageously applied particularly to a case where an optical disk of a type having information recorded at a constant linear velocity is reproduced at a constant angular velocity, it can also be suitably applied to other cases, such as where an optical disk of a type having information recorded at a constant linear velocity is reproduced at a constant linear velocity, to permit appropriate reproduction without being adversely influenced by a warp etc. of the optical disk.
According another aspect of the present invention, there is provided an optical disk reproduction apparatus which comprises: a rotation control arranged to drive an optical disk, having information recorded at a constant linear velocity, at a constant angular velocity; an optical pickup arranged to read out recorded information from the optical disk; a waveform equalization section arranged to perform a waveform equalization process on a reproduced RF signal that is generated on the basis of the recorded information read out by the optical pickup; a jitter detection section arranged to detect jitter of the reproduced RF signal having been subjected to the waveform equalization process; and a control section. The control section performs test reproduction of the optical disk with respect to a single testing radial location of the optical disk prior to actual reproduction of the optical disk, adjusts a waveform equalization characteristic of the waveform equalization section to an optimal setting so as to optimize jitter of a reproduced RF signal detected by the jitter detection section at the single testing radial location, and during the actual reproduction of the optical disk, adjusts the waveform equalization characteristic of the waveform equalization section to an optimal setting that is predicted, on the basis of a variation, in the linear velocity, relative to the testing radial location, in accordance with a radial position, on the optical disk, of each location to be reproduced via the optical pickup. In the case where an optical disk of a type having information recorded at a constant linear velocity is reproduced at a constant angular velocity, an optimal setting of the waveform equalization characteristic is predicted and set, for each radial position of the optical disk, on the basis of the optimal setting determined by the test reproduction, and thus there can always be provided an optimal waveform equalization characteristic, for each radial position of the optical disk, capable of optimizing (e.g., minimizing) the jitter. Further, because the test reproduction is performed with respect to only one predetermined testing radial location, such as the innermost or near-innermost location, of the optical disk, the present invention can significantly reduce the time required for the test reproduction.
In the above-mentioned invention, the control section may store, into a memory, the optimal setting of the waveform equalization characteristic determined by the test reproduction so that during the actual reproduction, the control section can arithmetically predict an optimal setting of the waveform equalization characteristic, on the basis of the optimal setting of the waveform equalization characteristic stored in the memory, in accordance with the radial position, on the optical disk, of each reproduced location.
According to still another aspect of the present invention, there is provided an optical disk reproduction apparatus which comprises: an optical pickup arranged to read out recorded information from an optical disk; a waveform equalization section arranged to perform a waveform equalization process on a reproduced RF signal that is generated on the basis of the recorded information read out by the optical pickup; a demodulation section arranged to demodulate the reproduced RF signal having been subjected to the waveform equalization process, while cumulatively storing the reproduced RF signal into a buffer memory; a jitter detection section arranged to detect jitter of the reproduced RF signal having been subjected to the waveform equalization process; a focus servo control section arranged to perform focus servo control by detecting a focus error on the basis of two focus-error-detecting signals that are generated on the basis of the recorded information read out by the optical pickup; a focus adjustment section arranged to perform a focus adjustment process for adjusting either one or both of a focus balance and focus offset by use of the two focus-error-detecting signals; a low-frequency-component detection section arranged to detect a low-frequency component in a focus drive signal produced by the focus servo control section; and a control section. When it is determined that the low-frequency component in the focus drive signal has exceeded a predetermined threshold value or a difference in the low-frequency component in the focus drive signal between an innermost location and a reproduced location of the optical disk has exceeded a predetermined threshold value and/or the jitter of the reproduced RF signal has exceeded a predetermined threshold value and also on condition that more than a predetermined quantity of data are currently being stored in the buffer memory, the control section suspends the readout operation of the optical pickup and adjusts the focus adjustment section so as to optimize the jitter of the reproduced RF signal detected by the jitter reproduction section. Then, the control section resumes the readout operation of the optical pickup after the adjustment to the focus adjustment section. Because the control section makes the jitter adjustment by suspending the readout operation of the optical pickup when the low-frequency component in the focus drive signal (corresponding to a warp of the optical disk) or the jitter level has become excessive and on condition that more than a predetermined quantity of data are currently being stored in the buffer memory, the inventive optical reproduction apparatus can appropriately reproduce even a warped optical disk with the jitter level optimized while maintaining the continuity of the reproduction.
In this case, the control section may perform control, after the adjustment to the focus adjustment section, to adjust the waveform equalization characteristic to an optimal setting so as to optimize the jitter of the reproduced RF signal detected by the jitter reproduction section and then may perform further control to resume the readout operation of the optical pickup after the adjustment of the waveform equalization characteristic. Further, the control section may perform control to suspend the above-mentioned adjustment when a predetermined cause for suspending the adjustment occurs during the course of the adjustment, and then may resume the readout operation of the optical pickup by returning to a previous setting that was being used prior to the adjustment. Thus, in a situation where the buffer memory gets empty due to some reason so that the continuity of the reproduction can not be maintained any longer, for example, it is possible to keep the continuity of the reproduction by suspending the adjustment operation.